Leaf rolling is evident in many corn fields this past week as temperatures continued hot and rainfall was scarce. Leaf rolling obviously reflects plant moisture deficits, but how significant is it as an indicator of corn plant stress?
As plant moisture content declines, the corn plant often 'protects' itself from excessive plant moisture loss (transpiration) by rolling its leaves. The rolled leaf offers less exposed surface area and transpiration is reduced. Thus, the act of leaf rolling is a sort of defensive posture by the corn plant against dry weather. In fact, one should probably prefer a hybrid whose leaves roll readily over one that remains unrolled during times of severe plant moisture deficits.
The recent hot, dry weather is causing parts of fields to exhibit leaf rolling. In many fields, the pattern of leaf rolling is fairly random across fields, often reflecting the existence of severe soil compaction. Soil moisture in compacted soil layers is much less available to the plants' roots than in uncompacted soil. Leaf rolling, therefore, occurs more quickly in compacted areas of fields. Yield is not likely affected yet in these compacted areas of fields, but continued hot, dry weather over the next two to three weeks could definitely affect these areas first.
Leaf rolling in the heat of the day does not mean that grain yield will be reduced. Remember, it is a defensive posture by the corn plant. If true drought conditions occur and the leaf rolling persists for 12 to 18 hours a day, then the corn plant is truly under drought stress and grain yield may be reduced. I don't believe, however, that such stress is occurring yet around the state.
In addition, the effects of drought stress on corn are most significant two weeks before to two weeks after pollination. Except for portions of southwest Indiana where some planting began in early April, most of the state's corn crop is nowhere near the critical pollination stage.